This invention relates to a cleaning device which is applied to an image forming machine, such as an electrostatic copier, a laser printer, or a facsimile, especially, an image forming machine equipped with an a-Si-based (amorphous silicon-based) photoconductor drum.
Image forming machines, for example, printers, using an a-Si-based photoconductor drum have been put to practical use. An a-Si material as a photoconductor is characterized by relative hardness and a long life, but after long-term use, is prone to leakage of electric charges, causing a disturbance to a toner image. To prevent this disturbance in the toner image, a cleaning roller is disposed in a cleaning device, and is in constant contact under pressure with the surface of a photoconductor drum to polish the surface of the photoconductor drum. The cleaning roller is formed from foamed synthetic rubber. A cleaning device provided with such a cleaning roller is disclosed, for example, in Japanese Unexamined Patent Publication No. 2000-112309. The cleaning device disclosed in this publication comprises a pair of arm members each having an intermediate portion pivotable about a support shaft, a cleaning roller rotatably supported between the front ends of the arm members via a shaft, helical tension springs for urging the other ends of the arm members so as to bring the cleaning roller into contact under pressure with the surface of an a-Si-based photoconductor drum, a drive gear integral with the photoconductor drum, and a driven gear integral with the cleaning roller and in mesh with the drive gear. A straight line connecting the support shaft (fulcrum) in each of the arm members and the shaft (point of action) of the cleaning roller is placed on a line nearly parallel to the line of action at the point of engagement between the drive gear and the driven gear (i.e., the line of action in the direction of transmission of force). A configuration in which the position of this support shaft (fulcrum) is slightly displaced from the parallel line is also disclosed in the publication.
In a printer having the cleaning device disclosed in the above-mentioned publication, a sheet transport passage extending through a transfer zone of the photoconductor drum may be disposed so as to extend substantially in an up-and-down direction in the transfer zone. In this case, the printing time from the start of printing to the completion of printing can be shortened, because the total length of the sheet transport passage is smaller than when the sheet transport passage is disposed so as to extend substantially in a lateral direction (horizontal direction) in the transfer zone. As a result, the long life and high speed of the printer can both be achieved. However, if the sheet transport passage is disposed in the cleaning device so as to extend substantially in the up-and-down direction in the transfer zone, the cleaning device is placed above the photoconductor drum. The support shaft (fulcrum) in each of the arm members, the other end of each of the arm members, and the helical tension springs urging the other ends are arranged downstream, in the direction of rotation of the photoconductor drum, from the position of the photoconductor drum in contact under pressure with the cleaning roller. Thus, they interfere with toner transport means disposed in the same region. To avoid this drawback, the support shaft (fulcrum) in each of the arm members has been placed upstream, in the direction of rotation of the photoconductor drum, from the position of the photoconductor drum in contact under pressure with the cleaning roller. In this case, it has been confirmed that an irregular drive due to a driving force by the drive gear occurs. Thus, a further improvement has been demanded.
An object of the present invention is to provide a novel cleaning device of an image forming machine, which prevents the occurrence of the irregular drive and permits compactness of the structure.
Another object of the present invention is to provide a novel cleaning device of an image forming machine, which prevents the occurrence of the irregular drive, permits compactness of the structure, and achieves both of the long life and high speed of the image forming machine.
According to the present invention, there is provided a cleaning device of an image forming machine, comprising:
a pair of arm members each having one end portion pivotable about a support shaft;
a cleaning roller rotatably supported between front end portions of the arm members via a shaft;
spring means for urging each of the arm members so as to bring the cleaning roller into contact under pressure with a surface of a photoconductor drum;
a drive gear integral with the photoconductor drum; and
a driven gear integral with the shaft of the cleaning roller and in mesh with the drive gear, and wherein
each of the arm members is disposed axially outwardly of the photoconductor drum, and
a center of the support shaft of each of the arm members is either placed on an extension of a line of action passing a point of engagement between the drive gear and the driven gear, or placed on an extension of a straight line passing the point of engagement, the straight line being within an angular range of some angle to the line of action.
Preferably, the center of the support shaft of each of the arm members is placed on the extension of the straight line passing the point of engagement, the straight line being within the angular range of xc2x110xc2x0 to the line of action.
Preferably, the drive gear is disposed at one end in the axial direction of the photoconductor drum, one of the arm members is disposed axially outwardly of the drive gear, and the driven gear is disposed in a region in the shaft of the cleaning roller which is located between the one arm member and one end in the axial direction of the cleaning roller.
Preferably, the spring means comprise a pair of helical compression springs, and each of the helical compression springs is disposed so as to act on a region in the corresponding arm member which is located between the support shaft and the shaft of the cleaning roller.
Preferably, a sheet transport passage passing through a transfer zone of the photoconductor drum extends substantially in an up-and-down direction in the transfer zone, the shaft of the cleaning roller is disposed downstream from the transfer zone of the photoconductor drum and above the photoconductor drum, toner transport means is disposed downstream, in the direction of rotation of the photoconductor drum, from a position of the photoconductor drum in contact under pressure with the cleaning roller, and is disposed above the photoconductor drum, and the support shaft of each of the arm members is disposed upstream, in the direction of rotation of the photoconductor drum, from the position of the photoconductor drum in contact under pressure with the cleaning roller.